1. **Problem Statement:** Verify that $(x+3)$ is a factor of $f(x) = 3x^3 + 2x^2 - 19x + 6$, find the remaining factors, write the complete factorization, and list all real zeros.
2. **Step 1: Verify the factor $(x+3)$**
Use the Factor Theorem: if $(x+3)$ is a factor, then $f(-3) = 0$.
Calculate:
$$f(-3) = 3(-3)^3 + 2(-3)^2 - 19(-3) + 6 = 3(-27) + 2(9) + 57 + 6 = -81 + 18 + 57 + 6 = 0$$
Since $f(-3) = 0$, $(x+3)$ is indeed a factor.
3. **Step 2: Find the remaining factor(s)**
Divide $f(x)$ by $(x+3)$ using polynomial long division or synthetic division.
Using synthetic division:
- Write coefficients: $3, 2, -19, 6$
- Use root $-3$:
$$\begin{array}{r|rrrr}
-3 & 3 & 2 & -19 & 6 \\
& & -9 & 21 & -6 \\
\hline
& 3 & -7 & 2 & \cancel{0} \\
\end{array}$$
The quotient is $3x^2 - 7x + 2$.
4. **Step 3: Factor the quadratic $3x^2 - 7x + 2$**
Find two numbers that multiply to $3 \times 2 = 6$ and add to $-7$: these are $-6$ and $-1$.
Rewrite:
$$3x^2 - 6x - x + 2 = 3x(x - 2) -1(x - 2) = (3x - 1)(x - 2)$$
5. **Step 4: Write the complete factorization**
$$f(x) = (x + 3)(3x - 1)(x - 2)$$
6. **Step 5: List all real zeros**
Set each factor equal to zero:
- $x + 3 = 0 \Rightarrow x = -3$
- $3x - 1 = 0 \Rightarrow x = \frac{1}{3}$
- $x - 2 = 0 \Rightarrow x = 2$
So the real zeros are:
$$x = -3, \frac{1}{3}, 2$$
7. **Step 6: Confirm with graphing utility**
The graph crosses the x-axis at these points, confirming the zeros.
Final answers:
- Remaining factors: $(3x - 1), (x - 2)$
- Complete factorization: $f(x) = (x + 3)(3x - 1)(x - 2)$
- Real zeros: $-3, \frac{1}{3}, 2$
Factor Verification 64E076
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